Resonance is one of the most common in the nature of physical phenomena.The resonance phenomenon can be observed in the mechanical, electrical and thermal systems even.Without resonance, we would not have radio, television, music and even swings at the playground, not to mention effective diagnostic systems used in modern medicine.One of the most interesting and useful kinds of resonance in a resonance circuit voltages.
resonant circuit elements
resonance phenomenon may occur in the so-called RLC-circuit comprising the following components:
- R - resistors.These devices related to the so-called active elements of the electrical circuit, electrical energy is converted into heat.In other words, they are removed from the circuit and the energy is converted into heat.
- L - inductance.Inductance in electrical circuits - analogue mass or inertia in mechanical systems.This component is not very noticeable in the circuit until you try to do it any changes.In mechanics, for example, such a change is the change in velocity.The electric circuit - the current change.If it for some reason happens inductance resists this change mode circuit.
- C - designation for capacitors, which are devices that store electrical energy, just as the spring maintains mechanical energy.Inductance concentrates and stores magnetic energy, while the capacitor charge concentrates and thus stores the electric energy.
concept of resonant circuit
key elements of the resonant circuit is the inductance (L) and capacitance (C).Resistor tends to damping of oscillations, so it removes power from the circuit.In reviewing the processes occurring in the resonant circuit, we temporarily ignore, but it must be remembered that, like the force of friction in mechanical systems, electrical resistance in the circuits can not be eliminated.
voltage resonance and current resonance
Depending on the method of joining key elements of the resonant circuit can be serial and parallel.When you connect a serial oscillating circuit to a voltage source with a frequency signal, which coincides with the natural frequency, under certain conditions, it appears the stress response.Resonance in the circuit with parallel-connected reactive elements called resonance currents.
natural frequency of the resonant circuit
We can make the system oscillate with its own frequency.To do this, you first need to charge the capacitor, as shown in the top picture on the left.When this is done, the key is transferred to the position shown in the same figure on the right.
At time "0", all the electrical energy stored in the capacitor, and the current in the circuit is equal to zero (figure below).Note that the upper plate of the capacitor is positively charged, and the lower - negative.We can not see the oscillations of the electrons in the circuit, but we can measure current ammeter, and with oscilloscope to trace the dependence of the current time.Note that T on our schedule - the time it takes to complete one oscillation bearing in electrical engineering called "the period of oscillation."
current flows in a clockwise direction (figure below).Energy is transferred from the capacitor to the coil inductance.At first glance it may seem strange that the inductance provides energy, but it looks like the kinetic energy contained in the moving mass.
flow of energy back into the condenser, but note that the polarity of the capacitor is now changed.In other words, the lower plate now has a positive charge, and a top plate - a negative charge (see Figure below).
system is now fully addressed, and the energy begins to flow from the condenser back to the inductance (see Figure below).As a result, energy is completely back to its starting point and is ready to start the cycle again.
oscillation frequency can be approximated as follows:
- F = 1 / 2π (LC) 0,5,
where: F - frequency, L - inductance, C - capacity.
consideration at this example, the process reflects the physical essence of the resonance voltage.
Research voltage resonance
In real LC circuits there is always a slight resistance, which decreases with each cycle increase in the amplitude of the current.After several cycles, the current is reduced to zero.This effect is called "damping of sinusoidal signal".The rate of current decay to zero depends on the resistance in the circuit.However, the resistance does not change the oscillation frequency of the resonant circuit.If the resistance is large enough, sinusoidal oscillations in the loop will not occur at all.
Obviously, where there is a natural frequency, there is a possibility of resonant excitation process.We do this in a series circuit including the power supply alternating current (AC), as shown on the left.The term "variable" means that the output voltage of the power varies with a certain frequency.If the frequency of the power supply coincides with the natural frequency of the circuit, a resonance voltage.
Terms appearance
We consider the resonance condition of stress.As shown in the latter figure, we returned to the resistor circuit.With no resistor in the circuit current in the resonant circuit will increase to a maximum value determined by the parameters of the circuit elements and the power supply.Increasing the resistance of the resistor in the resonance circuit increases the tendency to the attenuation of the current in the circuit, but does not affect the frequency of resonance vibrations.Typically, the mode voltage resonance does not occur if the impedance of the resonance circuit satisfies R = 2 (L / C) 0,5.
Using voltage resonance for radio transmission
Resonance stress is not only curious physical phenomenon.It plays a crucial role in wireless communications technology - radio, television, cellular telephony.Transmitters used for wireless transmission of information, compulsorily contain circuitry to resonate at a specific frequency for each device, called the carrier frequency.Using the transmitting antenna connected to the transmitter, it emits electromagnetic waves at the carrier frequency.
antenna at the other end of the transceiver path receives the signal and delivers it to the receiving circuit designed to resonate at the carrier frequency.It is obvious that the antenna receives a plurality of signals at different frequencies, not to mention the background noise.Thanks for the input receiver tuned to the carrier frequency of the resonant circuit, the receiver selects the correct frequency only, sifting out all unnecessary.
After detecting the amplitude modulated (AM) radio, isolated from a low-frequency signal (LF) is amplified and fed to the sound source.This is the simplest form of radio is very sensitive to noise and interference.
to improve the quality of the received information developed and successfully used by other, more advanced methods of radio transmission, which is also based on the use of tuned resonant systems.
frequency modulation or FM-radio solves many of the problems with the broadcast of amplitude-modulated transmission signal, but at the cost of considerable complication of the transmission system.In the FM-radio system sounds electronically tract become small changes in carrier frequency.A piece of equipment that performs this conversion is called a "modulator" is used with the transmitter.
Accordingly, the receiver must be added to a demodulator for converting the signal back into a form that can be reproduced through the loudspeaker.
Other examples of the use of the resonance voltage
voltage resonance as a fundamental principle laid down in many circuitry filters are widely used in electrical engineering to eliminate harmful and unnecessary signals, smoothing fluctuations and generate sinusoidal signals.
